A conventional reflective liquid crystal display device has been developed and spread as a display device operated with feeble power, and as information transmission medium such as a watch, a calculator, a cellular, a compact portable device, or various home electric products. As display modes, various types such as a TN (twisted nematic) type, an STN (super twisted nematic) type, and a ferroelectric type have been devised. However, all the devices use polarizing plates. Actually, since 60% of incident light to a liquid crystal element are absorbed by the polarizing plate, a dark screen is obtained. A resultant display is far from an ideal reflective display, e.g., a black display on a white background which can be easily seen.
In particular, a reflective color liquid crystal display device reflects a maximum of 10% or less of incident external light being incident on the display device to perform a display because of light absorption of the polarizing plate and a color filter. A resultant display is very dark, and is far from a vivid bright color display such as a display on print.
In recent years, as a method of solving the above drawback and realizing a bright color display without using a polarizing plate, a prior art 1 (Japanese Unexamined Patent Publication No. 6-294952) is proposed to attract attentions. In this propose, a mixture of a liquid crystal material and a polymer material consisting of a photo-set resin is inserted between a pair of substrates, and a laser beam is irradiated on the substrates in two directions, i.e., the upper and lower directions, to cause the interference pattern of the two laser beams to form strong/weak fringes of light in the mixture layer of the liquid crystal and the polymer material. The polymer photo-setting resin is photo-set in the form of layers according to the strong/weak fringe pattern to realize a multi-layer film consisting of polymer photo-setting resin layer/liquid crystal layer/polymer photo-setting resin layer/liquid crystal layer, . . . . Light having a specific wavelength range is interference-reflected according to the principle of composite multi-layer film interference reflection. When a voltage is applied to the multi-layer film by electrodes on the inner surfaces of the pair of substrates, the molecular axis direction of liquid crystal molecules in the liquid crystal layer changes. Accordingly, the refraction factor of the liquid crystal layer also changes. Therefore, the conditions of the interference reflection cannot be satisfied, and reflected light intensity also changes. In this way, light modulation can be performed by a voltage, the device functions as a display device. In the display device mentioned above, since any polarizing plate is not used, bright colors can be obtained. In addition, by changing the wavelength or irradiation angle of the irradiated laser beam, an interference pitch can be freely selected to realize arbitrary display colors. The display device, especially, as a reflective color display device, is more excellent than a conventional TN or STN reflective color display device.
However, as the drawback of the display device, as described in a prior art 2 (ASIA DISPLAY '95 P603-606), since a layer consisting of a photo-setting resin is formed with interference by two laser beams, the interference pitch is highly accurate, and the wavelength width of interference-reflected light is very narrow. Therefore, the display has vivid colors, but lacks brightness as a reflective display is obtained. In general, white is most desirable as a background color of the reflective display. For this reason, the conditions of interference reflection must be satisfied throughout a wide wavelength range of visible light. However, in the prior arts 1 and 2, it is very difficult to continuously change the interference pitches of the upper and lower layers, and a bright white display cannot be obtained without any problem. The second problem is as follows. That is, although a boundary surface between the photo-setting resin and a liquid crystal layer is desirably flat (planer) to improve the strength of interference reflection, the photo-setting resin and the liquid crystal layer are in contact with each other having small unevenness as described in the prior art 2. Therefore, all of incident light do not cause interference reflection, and part of the light is transmitted, so that a brighter reflective display device cannot be realized.
A prior art 3 (Japanese Unexamined Patent Publication No. 4-178623) as another prior art, is described as an example of a bright reflective color display device with interference reflection without using a polarizing plate. In this prior art, a liquid crystal layer and SiO.sub.2 layer are laminated on each other, the thicknesses and refraction factors of the respective layers are set to fit the conditions of interference reflection to produce selective reflection of a specific wavelength. When a voltage is applied across upper and lower electrodes of the resultant structure, the refraction factor of the liquid crystal layer changes as described above, the conditions of interference reflection are not satisfied, and reflected light intensity changes. For this reason, a display function can be realized. The problems of this prior art are as follows. First, since a layer for causing interference reflection consists of only 3 layers, i.e., SiO.sub.2 /liquid crystal layer/SiO.sub.2, sufficient intensity of interference-reflected light cannot be obtained, and almost incident light is transmitted to be absorbed in the lower light-absorbing layer. For this reason, a reflective display device having sufficient brightness cannot be realized. In order to improve the intensity of reflected light, a composite multi-layer consisting of at least 10 layers, i.e., SiO.sub.2 film/liquid crystal layer/SiO.sub.2 film/liquid crystal layer/SiO.sub.2 film . . . is preferably used. However, in this prior art, it is very difficult to form the composite multi-layer film. More specifically, an SiO.sub.2 film cannot be directly formed on the liquid crystal layer. As illustrated in this prior art, a spacer layer is temporarily formed on the entire surface of the liquid crystal layer, and the SiO.sub.2 film is formed on the spacer layer. Thereafter, the spacer is removed by etching except only the peripheral portion, and then a liquid crystal is injected into the bubble portion from which the spacer is removed, thereby forming a liquid crystal layer. It is apparent that manufacture of a composite multi-layer film consisting of 10 or more layers with the above structure is not practical because of difficulty caused by the reason why an SiO.sub.2 film cannot be directly formed on the liquid crystal layer. In addition, in this prior art, since a liquid crystal is injected into a bubble portion from which a spacer is removed by overetching, an alignment process for aligning the liquid crystal molecular axis direction cannot be performed, and the molecular axis direction of the injected liquid crystal may form various domains. In general, in order to improve the intensity of interference-reflected light, it is important to accurately control the thickness and the refraction factor of the liquid crystal layer. In this prior art, as described above, it is difficult to accurately control the refraction factor, and sufficient intensity of interference-reflected light cannot be obtained. A reflective display device having uniformity and brightness cannot be realized without any problem.
As described above, according to the conventional technique, the following problems are posed to realize a brighter reflective liquid crystal display device. That is, the conditions of interference reflection is difficult to be satisfied in the wide wavelength band of a visible light wavelength range, and all of incident light is not interference-reflected, but part of the light is transmitted. In addition, it is difficult to accurately control the refraction factor, sufficient intensity of interference reflection cannot be obtained. As a result, a reflective display device having uniformity and brightness cannot be realized without any problem.
The present invention has been made to solve the above problems, and its object is to provide a bright display device having uniformity and high intensity of reflected light, a display device which is easier to see and can realize a achromatic display having a black display image on a white background or a color display having high contrast, and a method in which a composite multi-layer film consisting of 10 or more layers required to realize the display devices can be more easily manufactured at high accuracy.
[Disclosure Of Invention]
The first embodiment of the present invention is characterized in that a composite multi-layer film obtained by alternately laminating films and liquid crystal layers a plurality of times is held between one pair of substrates, and a voltage is applied to the composite multi-layer film to control the reflection factor of the composite multi-layer film.
The second embodiment is characterized in that light-diffusing means is arranged outside one of the substrates, and light-absorbing means is arranged outside the other of the substrates.
The third embodiment a smectic liquid crystal, a nematic liquid crystal, a nematic polymer liquid crystal, a smectic polymer liquid crystal, or a mixture thereof.
The fourth embodiment is characterized in that the liquid crystal layer consists of a discotic liquid crystal or a mixture of a discotic liquid crystal and a nematic liquid crystal.
The fifth embodiment is characterized in that the liquid crystal layer consists of nematic liquid crystal molecules, and the major axis of the liquid crystal molecules is arranged in a direction almost parallel to the substrates or the film when no voltage is applied.
The sixth embodiment is characterized in that the liquid crystal layer consists of nematic liquid crystal molecules, and the major axis of the liquid crystal molecules is arranged in a direction almost perpendicular to the substrates or the film when no voltage is applied.
The seventh embodiment is characterized in that the light-absorbing means absorbs light in an arbitrary wavelength range or in a wavelength range of a visible light region which is transmitted through the composite multi-layer film.
The eighth embodiment is characterized in that a composite multi-layer film obtained by alternately laminating films and liquid crystal layers a plurality of times is held between one pair of substrates having electrodes formed on the inner surfaces of the substrates, at least one intermediate substrate having electrodes formed on both surfaces of the intermediate substrate is interposed in an intermediate portion of the composite multi-layer film, and light-diffusing means is arranged outside one of the substrates and light-absorbing means is arranged outside the other of the substrates, respectively.
The ninth embodiment is characterized in that the thicknesses of the liquid crystal layers and the films are set such that the composite multi-layer film reflects lights having at least one part of wavelengths of the incident visible light region when no voltage is applied.
The tenth invention is characterized in that the thicknesses of the liquid crystal layers and the films are set such that the composite multi-layer film reflects lights having at least one part of wavelengths of the incident visible light region when a voltage is applied.
The eleventh embodiment is characterized in that at least one refractive factor of the refractive factors of the major and minor axis directions of liquid crystal molecules in the liquid crystal layer is almost made equal to the refractive factor of the film.
The twelfth embodiment is characterized in that the plurality of composite multi-layer films in which the layer thicknesses of the films and the thicknesses of the liquid crystal layers are equal to each other in each composite multi-layer film and the thicknesses of the films and the thicknesses of the liquid crystal layers are different from each other in different composite multi-layer films are laminated, so that a plurality of wavelengths of incident lights are reflected.
The thirteenth embodiment is characterized in that the plurality of composite multi-layer films in which the layer thicknesses of the films and the thicknesses of the liquid crystal layers are equal to each other in each composite multi-layer film and the thicknesses of the films and the thicknesses of the liquid crystal layers are different from each other in different composite multi-layer films are laminated, so that the layer thicknesses of the liquid crystal layers and the films are set such that the plurality of composite multi-layer films reflect red light, green light, and blue light.
The fourteenth embodiment is characterized in that electrodes for independently applying a voltage are arranged on the composite multi-layer films, respectively.
The fifteenth embodiment is characterized in that the liquid crystal layer consists of nematic liquid crystal molecules, and at least a composite multi-layer film which is set to reflect light of a polarized component in an almost major axis direction of the nematic liquid crystal molecules or a direction almost perpendicular to the major axis direction is included.
The sixteenth embodiment is characterized in that the film is a film which is almost optically uniaxial or a film which is drawn.
The seventeenth embodiment is characterized by including at least a composite multi-layer film formed by following step; the composite multi-layer film is divided into two blocks, the liquid crystal molecular major axis direction of the liquid crystal layer of the first block is made to be almost perpendicular to the liquid crystal molecular major axis of the liquid crystal layer of the second block, and the first and second block are laminated.
The eighteenth embodiment is characterized in that electrodes for independently applying a voltage are arranged on the first and second blocks, respectively.
The nineteenth embodiment is characterized in that the material of the liquid crystal layer is coated on at least one surface of the film surfaces, a plurality of films on which the liquid crystal material is coated are laminated by a roller to be integrated with each other, and thus the composite multi-layer film is formed.
The twentieth embodiment is characterized in that, when the films are laminated by the roller, in a state wherein the liquid crystal layer is heated to a predetermined temperature to decrease the viscosity of the liquid crystal layer, the films are integrated with each other.
The twenty-first embodiment is characterized in that a uniaxial drawing process is performed to the films in advance to obtain alignment function for aligning liquid crystal molecules.
The twenty-second embodiment is characterized in that the material of the liquid crystal layer is coated on the film surfaces, a plurality of films on which the liquid crystal material is coated are laminated by a roller to be integrated with each other, and then a drawing process is performed to the resultant structure by a rolling roller to make the thickness of the film and the thickness of the liquid crystal layer equal to predetermined values, thereby forming the composite multi-layer film.
The twenty-third embodiment is characterized in that conductivity is given to the film.
The twenty-fourth embodiment is characterized in that the composite multi-layer film is constituted by laminating at least 10 layers of the liquid crystal layers and the films.
The twenty-fifth embodiment is characterized in that the composite multi-layer film is constituted by laminating at least 21 layers of the liquid crystal layers and the films.
The twenty-sixth embodiment is the display device which comprises a composite multi-layer film in which films and liquid crystal layers are alternately laminated, and controls the reflection factor of the composite multi-layer film by applying a voltage to the composite multi-layer film, and is characterized in that a refractive factor n.sub.LC1(.lambda.n), in a major axis direction, and a refractive factor n.sub.LC2(.lambda.n), in a minor axis direction, of a liquid crystal used in the liquid crystal layers with respect to light having a predetermined wavelength (?n) and a refractive factor n.sub.F1(.lambda.n) and a refractive factor n.sub.F2(.lambda.n), in X- and Y-axis directions which are perpendicular to each other in the film surface, of the films with respect to light having the predetermined wavelength (.lambda.n) are set in at least one of combinations of films and liquid crystal layers, which are adjacent to each other, of the films and the liquid crystal layers of the composite multi-layer film, to satisfy the following conditions [1] and [2]: EQU [1] n.sub.LC1(.lambda.n) .gtoreq.n.sub.F1(.lambda.n), or n.sub.LC1(.lambda.n) .apprxeq.n.sub.F1(.lambda.n), and EQU [2] n.sub.LC2(.lambda.n) .apprxeq.n.sub.F2(.lambda.n), and n.sub.LC1(.lambda.n) &gt;n.sub.LC2(.lambda.n), n.sub.F1(.lambda.n) &gt;n.sub.F2(.lambda.n).
According to this embodiment, when the conditions [1] and [2] are satisfied, a transmission state is set with respect to light of an X-axis direction component and light of a Y-axis direction component of the light having the predetermined wavelength (.lambda.n). Reflection occurs when the refraction factor of the film and the refraction factor of the liquid crystal layer are different from each other. Since a liquid crystal generally changes in refraction factor when an applied voltage is changed, a reflection state can be set by changing the application state of the voltage, and light modulation can be performed by the voltage.
The twenty-seventh embodiment is characterized in that the n.sub.F1(.lambda.n), n.sub.LC2(.lambda.n), a thickness d.sub.LC of the liquid crystal layer, and a thickness d.sub.F of the film are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy at least one of the following conditions [3] and [4]: EQU [3] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [4] n.sub.LC2(.lambda.n) .multidot.d.sub.LC .ltoreq.(1/4+m/2).multidot..lambda.n, or n.sub.LC2(.lambda.n) .multidot.d.sub.LC .apprxeq.(1/4+m/2).multidot..lambda.n
(where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k and m are 0 or integers). PA1 (where k is 0 or an integer). PA1 (where k is 0 or an integer). PA1 (where m is 0 or an integer). PA1 (where m is 0 or an integer).
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [3] is satisfied. Reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [4] is satisfied. With respect to the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [2].
The twenty-eighth embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned (homogeneously aligned) in a direction almost horizontal with respect to the film and the X-axis direction, at least, near the film in applying no voltage, and the composite multi-layer film is set in a light transmission state in applying no voltage and set in a light reflection state in applying a voltage. According to this embodiment, the composite multi-layer film is set in a light transmission state with respect to both lights of the X-axis direction component and the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage. Strong reflection can be obtained with respect to the light of the X-axis direction component of the light having predetermined wavelength (.lambda.n) in applying a voltage, and a transmission state is set with respect to the light of the Y-axis direction component. As the liquid crystal layer, a layer having positive dielectric anisotropy (.DELTA..epsilon.) (.DELTA..epsilon.&gt;0) is preferably used.
The twenty-ninth embodiment is characterized in that the n.sub.LC1(.lambda.n), n.sub.LC2(.lambda.n), n.sub.F1(.lambda.n), and n.sub.F2(.lambda.n) are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following conditions [5] and [6]: EQU [5] n.sub.LC1(.lambda.n) .apprxeq.n.sub.F1(.lambda.n), and EQU [6] n.sub.LC2(.lambda.n) .apprxeq.n.sub.F2(.lambda.n).
According to this invention, when the liquid crystal is aligned to rarely have a pretilt angle to the film in applying no voltage, a high transmission factor is given to the liquid crystal with respect to the light of the X-axis direction component and the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage.
The thirtieth embodiment is characterized in that the liquid crystal is aligned to rarely have a pretilt angle with respect to the film in applying no voltage.
The thirty-first embodiment is characterized in that the n.sub.LC1(.lambda.n) and n.sub.F1(.lambda.n) are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following condition [7]: EQU [7] n.sub.LC1(.lambda.n) &gt;n.sub.F1(.lambda.n) .gtoreq.0.96.multidot.n.sub.LC1(.lambda.n).
When the liquid crystal is aligned to have a predetermined pretilt angle with respect to the film in applying no voltage, the refraction factor of the liquid crystal layer in the X-axis direction is smaller than the refraction factor n.sub.LC1(.lambda.n) of the liquid crystal in the major axis direction. For this reason, in the range of the condition [7], when n.sub.LC1(.lambda.n) and n.sub.F1(.lambda.n) are properly set depending on the pretilt angle, more preferably, when n.sub.F1(.lambda.n) is made almost equal to an average refraction factor of the liquid crystal layer in the X-axis direction with respect to the light having the predetermined wavelength (.lambda.n) in applying no voltage, the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be sufficiently transmitted through at least one combination of a film and a liquid crystal layer which are adjacent to each other. Therefore, in the display device of this invention, when the liquid crystal is aligned to have a pretilt angle, a high transmission factor is given with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage. A transmission factor higher than that obtained under the condition [2] can be obtained with respect to the light of the Y-axis direction component.
The thirty-second embodiment is characterized in that the liquid crystal is aligned to have a predetermined pretilt angle, preferably an angle of from 1.degree. to 40.degree., with respect to the film in applying no voltage.
The thirty-third embodiment is characterized in that the n.sub.F1(.lambda.n) is made almost equal to an average refractive factor, in the X-axis direction, of the liquid crystal layer with respect to light having the predetermined wavelength (.lambda.n) in applying no voltage, and the n.sub.F2(.lambda.n) is made almost equal to an average refractive factor, in the Y-axis direction, of the liquid crystal layer with respect to light having the predetermined wavelength (.lambda.n) in applying no voltage. With this arrangement, in applying no voltage, a high transmission factor can be obtained with respect to the light of the X-axis direction component and the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n).
The thirty-fourth invention is characterized in that the n.sub.F1(.lambda.n), n.sub.LC1(.lambda.n), n.sub.LC2(.lambda.n), the thickness d.sub.LC of the liquid crystal layer, and the thickness d.sub.F of the film are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy at least one of the following conditions [8] and [9]: EQU [8] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [9] n.sub.LC2(.lambda.n) .multidot.d.sub.LC .ltoreq.(1/4+m/2).multidot..lambda.n ?.ltoreq.{n.sub.LC2(.lambda.n) +0.6.multidot.(n.sub.LC1(.lambda.n) -n.sub.LC2(.lambda.n))}.multidot.d.sub.LC
According to this invention, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [8] is satisfied. Although many liquid crystal molecules are not completely perpendicular to the film in applying a voltage, in the range of the condition [9], when n.sub.LC2(.lambda.n) and d.sub.LC are properly set depending on an applied voltage, reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be strengthened. With respect to light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [2].
Thirty-fifth embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned (homeotropically aligned) in a direction almost perpendicular to the film, at least, around the central portion of the liquid crystal layer in the direction of lamination in applying no voltage, and the composite multi-layer film is set in a light transmission state in applying a voltage and set in a light reflection state in applying no voltage. According to this embodiment, the composite multi-layer film is set in a light transmission state with respect to both lights of the X-axis direction component and the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying a voltage. Strong reflection can be obtained with respect to the light of the X-axis direction component of the light having predetermined wavelength (.lambda.n) in applying no voltage, and a transmission state is set with respect to the light of the Y-axis direction component. As the liquid crystal layer, a layer having negative dielectric anisotropy (.DELTA..epsilon.) (.DELTA..epsilon.&lt;0) is preferably used.
The thirty-sixth embodiment is characterized in that the n.sub.LC1(.lambda.n), n.sub.LC2(.lambda.n), and n.sub.F1(.lambda.n) are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following condition [10]: EQU [10] n.sub.LC1(.lambda.n) &gt;n.sub.F1(.lambda.n).gtoreq. n.sub.LC1(.lambda.n) -0.6.multidot.(n.sub.LC1(.lambda.n) -n.sub.LC2(.lambda.n)).
According to the thirty-fifth embodiment although a light transmission state is set with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying a voltage, many liquid crystal molecules are not completely horizontal with respect to the film in applying a voltage. For this reason, according to the thirty-sixth embodiment, in the range of the condition [10], when n.sub.LC1(.lambda.n) and n.sub.F1(.lambda.n) are properly set depending on the applied voltage, more preferably, when n.sub.F1(.lambda.n) is made almost equal to an average refraction factor of the liquid crystal layer in the X-axis direction with respect to the light having the predetermined wavelength (.lambda.n) in applying a voltage, the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be sufficiently transmitted through at least one combination of a film and a liquid crystal layer which are adjacent to each other. With respect to light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [2].
The thirty-seventh embodiment is characterized in that the n.sub.F1(.lambda.n) is made almost equal to an average refractive factor in the X-axis direction, of the liquid crystal layer with respect to light having the predetermined wavelength in applying a voltage.
The thirty-eighth embodiment is characterized in that the n.sub.F1(.lambda.n), n.sub.LC2(.lambda.n), the thickness d.sub.LC of the liquid crystal layer, and the thickness d.sub.F of the film are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy at least one of the following conditions [11] and [12]: EQU [11] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [12] n.sub.LC2(.lambda.n) .multidot.d.sub.LC .apprxeq.(1/4+m/2).multidot..lambda.n
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [11] is satisfied. Reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [12] is satisfied. With respect to the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [2]. In this display device, when the major axis of liquid crystal molecules used in the liquid crystal layer is aligned in a direction almost perpendicular to the film near the film in applying no voltage, reflection caused by at least one of the film and the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened.
The thirty-ninth embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned in a direction almost perpendicular to the film near the film in applying no voltage.
The fortieth embodiment is characterized in that the n.sub.LC2(.lambda.n) and d.sub.LC are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following conditions [13] and [14]: EQU [13] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [14] n.sub.LC2(.lambda.n) .multidot.d.sub.LC &lt;(1/4+m/2).multidot..lambda.n??.ltoreq.1.12n.sub.LC2(.lambda.n) .multidot.d.sub.LC
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [13] is satisfied. When the major axis of liquid crystal molecules used in the liquid crystal layer is aligned at a predetermined angle from a direction perpendicular to the film near the film in applying no voltage, the refraction factor of the liquid crystal layer in the X-axis direction is larger than the refraction factor n.sub.LC2(.lambda.n) of the liquid crystal in the minor axis direction. For this reason, in the range of the condition [14], when n.sub.LC2(.lambda.n) and d.sub.LC are properly set depending on an inclination of the liquid crystal molecules from the vertical direction in applying no voltage, reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage can be strengthened. With respect to the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [2].
The forty-first embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned to be inclined at a predetermined angle, preferably an angle of from 1.degree. to 40.degree., from a direction perpendicular to the film near the film in applying no voltage.
The forty-second embodiment is a display device which comprises a composite multi-layer film in which films and liquid crystal layers are alternately laminated, and controls the reflection factor of the composite multi-layer film by applying a voltage to the composite multi-layer film, and is characterized in that a refractive factor n.sub.LC1(.lambda.n), in a major axis direction, and a refractive factor n.sub.LC2(.lambda.n), in a minor axis direction, of a liquid crystal used in the liquid crystal layers with respect to light having a predetermined wavelength (.lambda.n) and a refractive factor n.sub.F1(.lambda.n) and a refractive factor n.sub.F2(.lambda.n), in X- and Y-axis directions which are perpendicular to each other in the film surface, of the films with respect to light having the predetermined wavelength (.lambda.n) are set in at least one of combinations of films and liquid crystal layers, which are adjacent to each other, of the films and the liquid crystal layers of the composite multi-layer film, to satisfy the following conditions [15] and [16]: EQU [15] n.sub.F1(.lambda.n) .gtoreq.n.sub.LC2(.lambda.n), or n.sub.F1(.lambda.n) .apprxeq.n.sub.LC2(.lambda.n), and EQU [16] n.sub.LC2(.lambda.n) .apprxeq.n.sub.F2(.lambda.n), and n.sub.LC1(.lambda.n) &gt;n.sub.LC2(.lambda.n).
According to this embodiment the composite multi-layer film is set in a transmission state with respect to both the lights of the X-axis direction component and the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) when the conditions [15] and [16] are satisfied. Reflection occurs when the refraction factor of the film and the refraction factor of the liquid crystal layer are different from each other. Since a liquid crystal generally changes in refraction factor when an applied voltage is changed, a reflection state can be set by changing the application state of the voltage, and light modulation can be performed by the voltage.
The forty-third embodiment is characterized in that the n.sub.F1(.lambda.n), n.sub.LC1(.lambda.n), a thickness d.sub.LC of the liquid crystal layer, and a thickness d.sub.F of the film are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy at least one of the following conditions [17] and [18]: EQU [17] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [18] n.sub.LC1(.lambda.n) .multidot.d.sub.LC .gtoreq.(1/4+m/2).multidot..lambda.n, or n.sub.LC1(.lambda.n) .multidot.d.sub.LC .apprxeq.(1/4+m/2).multidot..lambda.n
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [17] is satisfied. Reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [18] is satisfied. With respect to the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [16].
The forty-fourth embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned (homogeneously aligned) in a direction almost horizontal with respect to the film and aligned in the X-axis direction, at least, near the film in applying no voltage, and the composite multi-layer film is set in a light transmission state in applying a voltage and set in a light reflection state in applying no voltage. According to the present invention, the composite multi-layer film is set in a light transmission state with respect to both lights of the X-axis direction component and the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying a voltage. Strong reflection can be obtained with respect to the light of the X-axis direction component of the light having predetermined wavelength (.lambda.n) in applying no voltage, and a transmission state is set with respect to the light of the Y-axis direction component. As the liquid crystal layer, a layer having positive dielectric anisotropy (.DELTA..epsilon.) (.DELTA..epsilon.&gt;0) is preferably used.
The forty-fifth embodiment is characterized in that the n.sub.LC1(.lambda.n), n.sub.LC2(.lambda.n), and n.sub.F1(.lambda.n) are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following condition [19]: EQU [19] n.sub.LC2(.lambda.n) &lt;n.sub.F1(.lambda.n) .ltoreq.n.sub.LC2(.lambda.n) +0.6(n.sub.LC1(.lambda.n) -n.sub.LC2(.lambda.n)).
According to the forty-fourth embodiment, although a light transmission state is set with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying a voltage, in many case, liquid crystal molecules are not completely horizontal with respect to the film in applying a voltage. In this case, the refraction factor of the liquid crystal layer in the X-axis direction is larger than the refraction factor n.sub.LC2(.lambda.n) of the liquid crystal in the minor axis direction. For this reason, as in the forty-fifth embodiment, in the range of the condition [19], when n.sub.LC2(.lambda.n) and n.sub.F1(.lambda.n) are properly set depending on the applied voltage, more preferably, when n.sub.F1(.lambda.n) is made almost equal to an average refraction factor of the liquid crystal layer in the X-axis direction with respect to the light having the predetermined wavelength (.lambda.n) in applying a voltage, the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be sufficiently transmitted through at least one combination of a film and a liquid crystal layer which are adjacent to each other. A transmission factor higher than that obtained under the condition [16] can be obtained with respect to the light of the Y-axis direction component.
The forty-sixth embodiment is characterized in that the n.sub.F1(.lambda.n) is made almost equal to an average refractive factor, in the X-axis direction, of the liquid crystal layer with respect to light having the predetermined wavelength in applying a voltage.
The forty-seventh embodiment is characterized in that the n.sub.F1(.lambda.n), n.sub.LC1(.lambda.n), the thickness d.sub.LC of the liquid crystal layer, and the thickness d.sub.F of the film are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy at least one of the following conditions [20] and [21]: EQU [20] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [21] n.sub.LC1(.lambda.n) .multidot.d.sub.LC .apprxeq.(1/4+m/2).multidot..lambda.n
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [20] is satisfied. Reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [21] is satisfied. With respect to the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [16]. In this display device, when the liquid crystal is aligned to rarely have a pretilt angle to the film in applying no voltage, reflection caused by at least one of the film and the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage is strengthened.
The forty-eighth embodiment is characterized in that the liquid crystal is aligned to rarely have a pretilt angle to the film in applying no voltage.
The forty-ninth embodiment is characterized in that the n.sub.LC1(.lambda.n) and d.sub.LC are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following conditions [22] and [23]: EQU [22] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [23] n.sub.LC1(.lambda.n) .multidot.d.sub.LC &gt;(1/4+m/2).multidot..lambda.n.gtoreq.0.96n.sub.LC1(.lambda.n) .multidot.d.sub.LC
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [22] is satisfied. When the liquid crystal is aligned to have a predetermined pretilt angle to the film in applying no voltage, the refraction factor of the liquid crystal layer in the X-axis direction is smaller than the refraction factor n.sub.LC1(.lambda.n) of the liquid crystal in the major axis direction. For this reason, in the range of the condition [23], when n.sub.LC1(.lambda.n) and d.sub.LC are properly set depending on the pretilt angle, reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be strengthened. With respect to the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [16].
The fiftieth embodiment is characterized in that the liquid crystal is aligned to have a predetermined pretilt angle, preferably an angle of from 1.degree. to 40.degree., to the film in applying no voltage.
The fifty-first embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned (homeotropically aligned) in a direction almost perpendicular to the film, at least, near the central portion of the liquid crystal layer in the direction of lamination in applying no voltage, and the composite multi-layer film is set in a light transmission state in applying no voltage and set in a light reflection state in applying a voltage. According to this embodiment, the composite multi-layer film is set in a light transmission state with respect to both lights of the X-axis direction component and the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage. Strong reflection can be obtained with respect to the light of the X-axis direction component of the light having predetermined wavelength (.lambda.n) in applying a voltage, and a transmission state is set with respect to the light of the Y-axis direction component. As the liquid crystal layer, a layer having negative dielectric anisotropy (.DELTA..epsilon.) (.DELTA..epsilon.&lt;0) is preferably used.
The fifty-second embodiment is characterized in that the n.sub.LC1(.lambda.n), n.sub.LC2(.lambda.n), n.sub.F1(.lambda.n), and n.sub.F2(.lambda.n) are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following condition [24]: EQU [24] n.sub.F1(.lambda.n) .apprxeq.n.sub.LC2(.lambda.n) .apprxeq.n.sub.F2(.lambda.n), and n.sub.LC1(.lambda.n) &gt;n.sub.LC2(.lambda.n).
According to this embodiment, when the major axis of liquid crystal molecules used in the liquid crystal layer is aligned in a direction almost perpendicular to the film near the film in applying no voltage, a high transmission factor is given with respect to the light of the X-axis direction component and the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n) in applying no voltage.
The fifty-third embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned in a direction almost perpendicular to the film near the film in applying no voltage.
The fifty-fourth embodiment is characterized in that the n.sub.LC2(.lambda.n) and n.sub.F1(.lambda.n) are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy the following condition [25]: EQU [25] n.sub.LC2(.lambda.n) &lt;n.sub.F1(.lambda.n) .ltoreq.1.12.multidot.n.sub.LC2(.lambda.n).
When the major axis of liquid crystal molecules used in the liquid crystal layer is aligned at a predetermined angle from a direction perpendicular to the film near the film in applying no voltage, the refraction factor of the liquid crystal layer in the X-axis direction is larger than the refraction factor n.sub.LC2(.lambda.n) of the liquid crystal in the minor axis direction. For this reason, in the range of the condition [25], when n.sub.LC2(.lambda.n) and n.sub.F1(.lambda.n) are properly set depending on an inclination of the liquid crystal molecules from the vertical direction in applying no voltage, more preferably, when n.sub.F1(.lambda.n) is made almost equal to an average refraction factor of the liquid crystal layer in the X-axis direction with respect to the light having the predetermined wavelength (.lambda.n) in applying no voltage, the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be sufficiently transmitted through at least one combination of a film and a liquid crystal layer which are adjacent to each other in applying no voltage. Therefore, in the display device of this invention, when the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned at a predetermined angle from a direction perpendicular to the film near the film in applying no voltage, a high transmission factor is given in applying no voltage with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n). A transmission factor higher than that obtained under the condition [16] can be obtained with respect to the light of the Y-axis direction component.
The fifty-fifth embodiment is characterized in that the major axis of the liquid crystal molecules used in the liquid crystal layer is aligned to be inclined at a predetermined angle, preferably an angle of from 1.degree. to 40.degree., from a direction perpendicular to the film near the film in applying no voltage.
The fifty-sixth embodiment is characterized in that the n.sub.F1.lambda.n) is made almost equal to an average refractive factor, in the X-axis direction, of the liquid crystal layer with respect to light having the predetermined wavelength (.lambda.n) in applying no voltage, and the n.sub.F2(.lambda.n) is made almost equal to an average refractive factor, in the Y-axis direction, of the liquid crystal layer with respect to light having the predetermined wavelength (.lambda.n) in applying no voltage. With this arrangement, in applying no voltage, a high transmission factor can be obtained with respect to the light of the X-axis direction component and the light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n).
The fifty-seventh embodiment is characterized in that the n.sub.F1(.lambda.n), n.sub.LC1(.lambda.n), n.sub.LC2(.lambda.n), the thickness d.sub.LC of the liquid crystal layer, and the thickness d.sub.F of the film are set in at least one of the combinations of films and liquid crystal layers, which are adjacent to each other, to satisfy at least one of the following conditions [26] and [27]: EQU [26] n.sub.F1(.lambda.n) .multidot.d.sub.F .apprxeq.(1/4+k/2).multidot..lambda.n, and EQU [27] n.sub.LC1(.lambda.n) .multidot.d.sub.LC .gtoreq.(1/4+m/2).multidot..lambda.n.gtoreq.{n.sub.LC1(.lambda.n) -0.6.multidot.(n.sub.LC1(.lambda.n) -n.sub.LC2(.lambda.n))}.multidot.d.sub.LC
According to this embodiment, reflection caused by the film with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) is strengthened when the condition [26] is satisfied. Although in many case, liquid crystal molecules are not completely perpendicular to the film in applying a voltage, in the range of the condition [27], when n.sub.LC1(.lambda.n) and d.sub.LC are properly set depending on an applied voltage, reflection caused by the liquid crystal layer with respect to the light of the X-axis direction component of the light having the predetermined wavelength (.lambda.n) can be strengthened. With respect to light of the Y-axis direction component of the light having the predetermined wavelength (.lambda.n), a transmission state is set according to the condition [16].
The fifty-eighth embodiment is characterized in that the n.sub.F1(.lambda.n), d.sub.F, and .lambda.n are set to satisfy the following condition [28]: EQU [28] (1/8+k/2).multidot..lambda.n.ltoreq.n.sub.F1(.lambda.n) .multidot.d.sub.F .ltoreq.(3/8+k/2).multidot..lambda.n
The fifty-ninth embodiment is characterized in that the n.sub.F2(.lambda.n), d.sub.F, and .lambda.n are set to satisfy the following condition [29]: EQU [29] (1/8+k/2).multidot..lambda.n.ltoreq.n.sub.F2(.lambda.n) .multidot.d.sub.F .ltoreq.(3/8+k/2).multidot..lambda.n
The sixtieth embodiment is characterized in that the .lambda.n, n.sub.LC2(.lambda.n), and d.sub.LC are set to satisfy the following condition [30]: EQU [30] (1/8+m/2).multidot..lambda.n.ltoreq.n.sub.LC2(.lambda.n) .multidot.d.sub.LC .ltoreq.(3/8+m/2).multidot..lambda.n
The sixty-first embodiment is characterized in that the .lambda.n, n.sub.LC1(.lambda.n), and d.sub.LC are set to satisfy the following condition [31]: EQU [31] (1/8+m/2).multidot..lambda.n.ltoreq.n.sub.LC1(.lambda.n) .multidot.d.sub.LC .ltoreq.(3/8+m/2).multidot..lambda.n
As in the display devices of the fifty-eighth to sixty-first embodiments, even if a wavelength to be reflected is offset from the predetermined wavelength .lambda.n by about (1/8).lambda.n, only the central wavelength of reflection is offset, and reflection itself occurs.
The sixty-second embodiment is characterized in that the plurality of films and the plurality of liquid crystal layers of the composite multi-layer film are designed to satisfy a condition described in one of the twenty-sixth to sixty-first inventions. As described above, in order to satisfy a condition described in one of the twenty-sixth to sixty-first inventions in the plurality of films and plurality of liquid crystal layers of the composite multi-layer film, it is preferable that the refraction factor n.sub.LC1(.lambda.n), in the major axis direction, of the refraction factor used in the liquid crystal layer with respect to the light having the predetermined wavelength (.lambda.n), the refraction factor n.sub.LC2(.lambda.n) in the minor axis direction, and the thickness d.sub.LC of the liquid crystal layer are almost the same in the plurality of liquid crystal layers, and that the refraction factor n.sub.F1(.lambda.n), in the X-axis direction, of the film with respect to the light having the predetermined wavelength (.lambda.n), the refraction factor n.sub.F2(.lambda.n) in the Y-axis direction, and the thickness d.sub.F of the film are the same in the plurality of films.
The sixty-third embodiment is characterized in that at least two composite multi-layer films which satisfy a condition described in one of the twenty-sixth to sixty-second embodiments with respect to the P and S waves of light having the predetermined wavelength (.lambda.n) are laminated, and a voltage is applied to the laminated composite multi-layer films to control the reflection factors of the laminated composite multi-layer film.
According to this embodiment, transmission and reflection can be controlled with respect to both P and S waves of the light having the predetermined wavelength (.lambda.n), a display device having a higher contrast can be realized.
The sixty-fourth embodiment is characterized in that a plurality of composite multi-layer films which satisfy a condition described in one of the twenty-seventh to sixty-second embodiments with respect to a plurality of different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) are laminated, and a voltage is applied to the plurality of laminated composite multi-layer films to control the reflection factors of the plurality of laminated composite multi-layer film.
The sixty-fifth embodiment is characterized in that a plurality of composite multi-layer films which satisfy a condition described in one of the twenty-sixth to sixty-second embodiments with respect to the P and S waves of lights having a plurality of different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) are laminated, and a voltage is applied to the plurality of laminated composite multi-layer films to control the reflection factors of the plurality of laminated composite multi-layer film.
In these display devices of the sixty-fourth and sixty-fifth embodiments, the plurality of composite multi-layer films comprise a plurality of films and a plurality of liquid crystal layers, and it is preferable that the refraction factor n.sub.LC1(.lambda.n), in the major axis direction, of the liquid crystal used in the liquid crystal layer with respect to the light having the predetermined wavelength (.lambda.n), the refraction factor n.sub.LC2(.lambda.n), in the minor axis direction, and the thickness d.sub.LC of the liquid crystal layer are almost the same in the plurality of liquid crystal layers in the same composite multi-layer film and are different in the different composite multi-layer films, and that the refraction factor n.sub.F1(.lambda.n), in the X-axis direction, of the film with respect to the light having the predetermined wavelength (.lambda.n), the refraction factor n.sub.F2(.lambda.n), in the Y-axis direction, and the thickness d.sub.F of the film are almost the same in the plurality of liquid crystal layers in the same composite multi-layer film and are different in the different composite multi-layer films.
The sixty-sixth embodiment is characterized in that the n.sub.LC1(.lambda.n) and n.sub.LC2(.lambda.n) are set with respect to the predetermined wavelength (.lambda.n) to satisfy the following condition [32]: EQU [32] n.sub.LC1(.lambda.n) /n.sub.LC2(.lambda.n) .gtoreq.1.10.
The sixty-seventh embodiment is characterized in that the n.sub.LC1(.lambda.n) and n.sub.LC2(.lambda.n) are set with respect to the plurality of different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) to satisfy the following condition [33]: EQU [33] n.sub.LC1(.lambda.n) /n.sub.LC2(.lambda.n) .gtoreq.1.10.
When the birefringence factor of the liquid crystal is given by n.sub.LC1(.lambda.n) /n.sub.LC2(.lambda.n) .gtoreq.1.10 as described above, even if the number of films and the number of liquid crystal layers are reduced, a high reflection factor can be obtained.
The sixty-eighth embodiment is characterized in that the sum of the number of films and the number of liquid crystal layers of the composite multi-layer film or the sum of the number of films and the number of liquid crystal layers of the plurality of laminated composite multi-layer films is set to be not less than 100. When the sum of the number of films and the number of liquid crystal layers is set to be 100 or more, a display device having a high reflection factor can be obtained.
The sixty-ninth embodiment is characterized in that the lights having the plurality of different predetermined wavelength (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) are lights having 3 to 12 different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L, 3.ltoreq.L.ltoreq.12), the n.sub.LC1(.lambda.n) and n.sub.LC2(.lambda.n) are set with respect to the lights having the 3 to 12 different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L, 3.ltoreq.L.ltoreq.12) to satisfy the following condition [34]: EQU [34] n.sub.LC1(.lambda.n) /n.sub.LC2(.lambda.n) .gtoreq.1.10, and
the sum of the number of films and the number of liquid crystal layers of the plurality of laminated composite multi-layer films is set to be about 100 to 400.
The seventieth embodiment is characterized in that the lights having the 3 to 12 different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) are lights having different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L, 3.ltoreq.L.ltoreq.12, where L is a multiple of three) whose number is a multiple of three. In the display devices of the seventieth and seventy-first embodiments, reflection conditions are satisfied for, e.g., red light, green light, and blue light, respectively, so that a white display can be easily realized.
The seventy-first embodiment is characterized in that the lights having the plurality of different predetermined wavelength (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) are lights having 4 to 8 different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L, where 4.ltoreq.L.ltoreq.8), the n.sub.LC1(.lambda.n) and n.sub.LC2(.lambda.n) are set with respect to the lights having the 4 to 8 different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L, 4.ltoreq.L.ltoreq.8) to satisfy the following condition [35]: EQU [35] n.sub.LC1(.lambda.n) /n.sub.LC2(.lambda.n) .gtoreq.1.13, and
the sum of the number of films and the number liquid crystal layers of the plurality of laminated composite multi-layer films is set to be about 100 to 300.
The seventy-second embodiment is characterized in that the lights having the plurality of different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) are visible lights.
The seventy-third embodiment is characterized in that light having at least one wavelength of the lights having the plurality of different predetermined wavelengths (.lambda.n=.lambda.1, .lambda.2, . . . , .lambda.L) is used as light having a wavelength in an infrared region. When the display device is obliquely viewed, a reflection wavelength shifts to a short wavelength side. Therefore, when a reflection wavelength range from the front distinct vision is enlarged to the infrared range, white reflection can be realized even if the display is viewed in any direction, i.e., viewed from the front or obliquely viewed. The reflection wavelength is preferably shifted to about 1,200 nm.